Introduction to the Silicoflagellata

Silicoflagellates are planktonic marine
chromists that are both
photosynthetic and heterotrophic. Their internal silica skeletons are
composed of a network of bars, and resemble those of
radiolarians but
are generally much less complex. Silicoflagellate skeletons usually
comprise 1-2% of the siliceous component of marine sediments; they are
thus much less abundant than
diatoms.
However, they are widely distributed throughout the world ocean. This
specimen of Dictyocha, shown above right, was recovered from
modern deep-sea sediments in the North Pacific.

Living silicoflagellates propel themselves with one long eukaryotic
flagellum, or undulipodium. The spines on the skeleton may function in
retarding sinking, which is of obvious importance to a photosynthetic
organism. Only asexual reproduction is known. Silicoflagellate skeletons
may vary considerably within a single species, making it difficult to
define species.

Silicoflagellates first appear in the Early
Cretaceous and become common
in the Late Cretaceous. They were somewhat more diverse in the early
Cenozoic than they are today.